Article formed of an aluminium bronze

ABSTRACT

A screw-threaded securing member is formed from an aluminium bronze alloy consisting by weight of 5 to 8% aluminium, up to 0.5% iron, 0.1 to 0.25% tin and/or silver, the balance being copper and any impurities.

United States Patent Ashton Sept. 16, 1975 [54] ARTICLE FORMED OF AN ALUMINIUM 2,829,971 4/1958 Klement 75/162 BRONZE 2,829,972 4/1958 Klement.... 75/162 3,725,056 1 4/1973 lngerson 75/154 [75] Inventor: Norman Coupe Ashton,

Huddersfield, England FOREIGN PATENTS OR APPLICATIONS Assigneel N. C. Ashton im ted Yorkshire, 360,250 1905 France 75/154 England OTHER PUBLICATIONS 22 Fiied; Sept 6, 1973 Metals Handbook, 8th Ed. V01. 1, 1961 pgs. 1033 &

[52] US. Cl. 75/154; 75/153; 75/162; 85/1 R; 29/183 [51] Int. Cl. C22c 9/00; C22c 9/02; F16b 35/00 [58] Field of Search 75/153, 154, 162; 148/115, 32; 85/1, 41

[56] References Cited UNITED STATES PATENTS 2,829,968 4/1958 Klement 75/162 2,829,969 4/1958 Klement 75/162 Prinwry Exuminer C. Lovell Attorney, Agent, or FirmNorris & Bateman ABSIRACT A screw-threaded securing member is formed from an aluminium bronze alloy consisting by weight of 5 to 8% aluminium, up to 0.5% iron, 01 to 0.25% tin and- /0r silver, the balance being-copper and any impurities.

5 Claims, N0 Drawings ARTICLE FORMED OF AN ALUMINIUM BRONZE This invention relates to securing members and more particularly to securing members formed of aluminium bronze.

Commercial alpha aluminium bronze normally contains between and 8% by weight of aluminium, small percentages of various alloying agents, such as iron, and the balance is copper plus any impurities. Iron has been added in quantities up to 3% to improve the granular structure and the tensile strength of the alloy.

It has also been proposed to add small percentages of tin and/or silver to the alloy to inhibit stress corrosion see for example United Kingdom Pat. No. 842,033 which describes a 5 to 8% aluminium bronze alloy comprising 0.005 to 0.60% tin and 0.005 to 0.69% silver. This known aluminium bronze alloy also contains 1.6 to 2.9% iron presumably to give the required grain structure and tensile strength, but it is believed that such an addition of iron leads to problems of stress cor rosion.

Securing members such as, for example, bolts which are subjected to stress in open air or corrosive conditions are particularly prone to stress corrosion and it is an object of this invention to form such members of a material which is less susceptible to stress corrosion and which has an adequate tensile strength and notch ductility.

According to this invention, a securing member is formed from an aluminium bronze alloy consisting by weight of s to 8% aluminium, up to 0.5% iron, 0.1 to 0.25% tin and/or silver, the balance being copper and any impurities.

Preferably, the securing member is screw-threaded and may comprise a bolt, set-screw, stud or like memher.

The present invention is based upon the discovery that advantage can be taken of the higher ductility of the basic alloy by omitting or at least reducing the iron content in order to facilitate subsequent cold working of the material. Thus it follows that the tensile strength can be increased to a greater extent by the cold working operation than is possible with the iron containing alloy and results in a material having a higher notch ductility.

The securing member is, preferably, cold formed from the alloy and the cold forming operation may include rolling, forging and thread rolling operations.

The alloy may include iron in the range 0.01 to 0.5% by weight and preferably the iron is present in the range 0.01 to 0.10% by weight as it has been found that the ductility increases with the reduction in the percentage of iron present and keeping the iron content to this lower end of the range produces a very ductile alloy.

In a preferred embodiment of this invention a hexagon headed screw-threaded bolt is produced from an aluminium bronze alloy by cold forming operations including rolling, forging and thread rolling operations. The aluminium bronze alloy from which the bolts are formed comprises by weight 7% aluminium, 0.10% iron, and 0.1% tin the balance being copper and the usual impurities. This alloy has a high ductility which enables the tensile strength to be increased by the cold working operations to a value of approximately 41 tons per square inch. It is also found that this alloy has a high notch ductility and tests upon a specimen bolt of this alloy resulted in an Izod test value of Ft. lbs.

The alloy therefore not only enables bolts to be formed by cold working operations and renders subsequent heat treatment unnecessary due to the high ductility of the alloy, but also results in bolts being formed which have greater tensile strength, higher notch ductility and improved stress corrosion resistance than bolts formed from the known aluminium bronze alloys containing by weight 1.6 to 2.9% iron.

The tin and/or silver is added to inhibit stress corrosion, so that the bolts formed from the alloy can be used in relatively corrosive conditions such as in outdoor locations on, for example, crash barriers on motorways. Generally, it is preferred to use tin rather than silver or mixtures of tin and silver, however, if there is an appreciable quantity of silver present in the copper then it may be possible to reduce the tin which has to be added by a corresponding amount.

In addition, the low iron content of this alloy facilitates the formation of bolts therefrom by hot working processes which bolts also have improved stress corrosion resistance. The presence of iron above the solubility limit of 0.75 to 1.0% by weight in the known alloy hereinbefore described results in the precipitation of an iron-rich second phase at the grain boundaries producing areas which are potential sites of stress concentration which can add to the working stresses in the material and lead to stress corrosion. Thus, it will be appreciated that the low iron content of the alloy in this preferred embodiment of the invention alleviates this.

problem as the formation of iron-irch precipitates in the material is reduced.

1 claim:

1. An integral screw threaded securing member such as a bolt or set screw having increased resistance to stress corrosion in open air and other corrosive environments formed from an aluminum bronze alloy consisting by weight of about 5 to 8% aluminum, up to about 0.5% iron, about 0.1 to 0.25% tin and/or silver, the balance being copper and any impurities.

2. A securing member according to claim 1, wherein the alloy includes iron in the range 0.01 to 0.5% by weight.

3. A securing member according to claim 2, wherein the alloy includes iron in the range 0.01 to 0.10% by weight.

4. A securing member according to claim 1, wherein the alloy comprises substantially 7% by weight of aluminium.

5. An integral screw threaded securing member such as a bolt or screw having increased resistance to stress corrosion in open air and other corrosive environments formed from an aluminum bronze alloy consisting of about 7% aluminum, about 0.10% iron. about 0.1% tin,

the balance being copper and any impurities. 

1. AN INTEGRAL SCREW THREADED SECURING MEMBER SUCB AS A BBOLT OR SET SCREW HVVING INCREASED RESISTANCE TO STRESS CORROSION IN OPEN AIR AND OTTHER CORROSIVE ENVIRONMENTS FORMED FROM AN ALUMINUM BONZE ALLOY CONSISTING BY WEIGHT OF ABOUT 5 TO 8% ALUMINUM, UP TO ABOUT 0.5% IRON, ABOUT 0.1 TO 0.25% TIN AND/OR SILVER, THE BLANCE BEING COPPER AND ANY IMPURITIES.
 2. A securing member according to claim 1, wherein the alloy includes iron in the range 0.01 to 0.5% by weight.
 3. A securing member according to claim 2, wherein the alloy includes iron in the range 0.01 to 0.10% by weight.
 4. A securing member according to claim 1, wherein the alloy comprises substantially 7% by weight of aluminium.
 5. An integral screw threaded securing member such as a bolt or screw having increased resistance to stress corrosion in open air and other corrosive environments formed from an aluminum bronze alloy consisting of about 7% aluminum, about 0.10% iron, about 0.1% tin, the balance being copper and any impurities. 